Autologous Growth Factors to Promote Tissue In-Growth in Vascular Device

ABSTRACT

Methods and devices for ameliorating stent graft migration and endoleak using treatment site-specific cell growth promoting compositions in combination with stent grafts are disclosed. Also disclosed is coating of autologous growth factor compositions onto stent grafts prior to stent graft implantation. Additional embodiments include stent grafts having autologous growth factor composition coatings useful for treating aneurysms.

RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 10/977,545, filed Oct. 28, 2004, which is herein incorporatedby reference in its entirety.

FIELD OF THE INVENTION

Methods and devices for preventing vascular device migration usingautologous growth factor composition-coated vascular devices aredisclosed. Specifically, methods for producing autologous growth factorcompositions and coating vascular devices with the compositions beforedevice implantation are provided.

BACKGROUND OF THE INVENTION

A variety of implantable vascular devices, including stent grafts andstents, have been developed to treat abnormalities of the vascularsystem. Stent grafts are used to treat aneurysms of the vascular systemand have also emerged as a new treatment for a related condition, acuteblunt aortic injury, where trauma causes damage to an artery. Stents areused to treat areas of vessel narrowing or atherosclerosis.

Aneurysms arise when a thinning, weakening section of vessel wallballoons out to more than 150% of its normal diameter. These thinned andweakened sections of vessel walls can burst, causing an estimated 32,000deaths in the United States each year. Additionally, aneurysm deaths aresuspected of being underreported because sudden unexplained deaths,about 450,000 in the United States alone, are often simply misdiagnosedas heart attacks or strokes while many of them may be due to aneurysms.

U.S. surgeons treat approximately 50,000 abdominal aortic aneurysms eachyear, typically by replacing the abnormal section of vessel with aplastic or fabric graft in an open surgical procedure. A less-invasiveprocedure that has more recently been used is the placement of a stentgraft at the aneurysm site. Stent grafts are tubular devices that spanthe aneurysm to provide support without replacing a section of thevessel. The stent graft, when placed within the artery at the aneurysmsite, acts as a barrier between blood flow and the weakened wall of theartery, thereby decreasing pressure on the damaged portion of theartery. This less invasive approach to treating aneurysms decreases themorbidity seen with conventional aneurysm repair. Additionally, patientswhose multiple medical comorbidities make them excessively high risk forconventional aneurysm repair are candidates for stent grafting.

Stents are rigid, or semi-rigid, tubular scaffoldings that are used totreat vessel narrowing or atherosclerosis, the leading cause of death inthe United States. Specifically, atherosclerosis and other forms ofcoronary artery narrowing are treated with percutaneous transluminalangioplasty (“angioplasty”). The objective of angioplasty is to enlargethe lumen of an affected vessel by radial hydraulic expansion. Theprocedure is accomplished by inflating a balloon within the narrowedlumen of the affected artery. After (or during) such an angioplastyprocedure, stents are deployed at the treatment site within the vesselto reduce the risks of reclosure. Stents are generally positioned acrossthe treatment site, and then expanded to keep the passageway clear. Thestent provides a scaffold which overcomes the natural tendency of thevessel walls of some patients to renarrow, thus maintaining the opennessof the vessel and resulting blood flow.

While stent grafts and stents (hereinafter collectively referred to as“vascular devices”) represent improvements over previously-used vesseltreatment techniques, there are still risks associated with them. Themost common of these risks is migration of the vascular device due tohemodynamic forces within the vessel. Stent graft migrations lead toendoleaks, a leaking of blood into the aneurysm sac between the outersurface of the graft and the inner lumen of the blood vessel. Stentmigration can leave a treated area of a vessel more susceptible toreclosure. Such migrations of vascular devices are especially possiblein curved portions of vessels where asymmetrical hemodynamic forces inthe area can place uneven forces on the vascular device. Additionally,the asymmetrical hemodynamic forces can cause remodeling of an aneurysmsac which leads to increased risk of aneurysm rupture and increasedendoleaks.

Based on the foregoing, one goal of treating aneurysms and vesselnarrowings is to provide vascular devices that do not migrate. Toachieve this goal, vascular devices with stainless steel anchoring barbsthat engage the vessel wall have been developed. Additionally,endostaples that fix vascular devices more readily to the vessel wallhave been developed. While these physical anchoring devices have provento be effective in some patients, improvements continue to be sought toassure the position of stent grafts once placed.

Additionally, the combination of the metal scaffolding of most stentgrafts and graft migration in a small percentage of cases has led to thecontraindication of magnetic resonance imaging (MRI) in some patientshaving stent grafts. The magnetic fields used in this imaging process,when moving across the body, may cause insufficiently fixatedmetal-containing stents to migrate.

One way to improve vascular device fixation is to administer to thetreatment site, either before, during or relatively soon afterimplantation, a cell growth-promoting factor. This administration can bebeneficial because, normally, the endothelial cells that make up theportion of the vessel to be treated are quiescent at the time ofvascular device implantation and do not multiply. As a result, thevascular device rests against a quiescent endothelial cell layer. Ifcell growth-promoting compositions are administered immediately before,during or relatively soon after vascular device deployment, the normallyquiescent endothelial cells lining the vessel wall, and in intimatecontact with the vascular device, will be stimulated to proliferate. Thesame will occur with smooth muscle cells and fibroblasts found withinthe vessel wall. As these cells proliferate they can grow into, onand/or around the vascular device such that the vascular device becomesphysically attached to the vessel lumen rather than merely restingagainst it. This endothelialization helps promote vascular devicefixation.

Endothelialization has been observed to naturally occur in some humanstent grafts within weeks of implantation. This naturalendothelialization is not complete or consistent, however, and thereforedoes not in some cases prevent the stent graft migration and endoleak.Methods to increase endothelialization are sought to improve clinicaloutcome after stent grafting.

Based on the above discussed issues, additional methods for fixatingstent grafts to vessel walls are needed to further prevent occurrencesof endoleaks and stent graft migration.

SUMMARY OF THE INVENTION

The risk of stent graft migration can be reduced by delivering to thetreatment site, as a coating on the stent graft, endothelializationfactors such as autologous growth factor compositions. Thisadministration can be beneficial because, normally, the endothelialcells that make up the portion of the vessel to be treated are quiescentat the time of stent graft implantation and do not multiply. As aresult, the stent graft rests against a quiescent endothelial celllayer. If autologous growth factor compositions are administered to thetreatment site with the stent graft deployment, the normally quiescentendothelial cells lining the vessel wall, and in intimate contact withthe stent graft, will be stimulated to proliferate. The same will occurwith smooth muscle cells and fibroblasts found within the vessel wall.As these cells proliferate they can grow into and around the stent graftlining such that the stent graft becomes physically attached to thevessel lumen rather than merely resting against it. Thisendothelialization helps to prevent stent graft migration. These methodscan promote healing, reduce endoleaks and minimize device migration bypromoting endothelial tissue in-growth.

Based on the foregoing, embodiments according to the present inventionprovide stent grafts having autologous growth factor compositions coatedthereon for the treatment of aneurysms, and associated methods for usingand/or manufacturing the stent grafts. Additionally, stent grafts aredisclosed which provide structural support for weakened arterial wallswhile the accompanying compositions promote tissue in-growth to reducethe chance of graft migration and endoleaks.

Therefore, embodiments according to the present invention providemethods for providing a stent graft and a cell growth-promotingcomposition comprising obtaining autologous platelet rich plasma (PRP)from a patient in need of a stent graft, activating the PRP to formautologous growth factor composition, coating the stent graft with theautologous growth factor composition and implanting the autologousgrowth factor composition-coated stent graft into a vessel at atreatment site in a patient wherein the autologous growth factorcomposition-coated stent graft induces endothelialization of the stentgraft.

In one embodiment of the method for providing a stent graft and a cellgrowth-promoting composition, the coating step comprises injectingautologous growth factor composition through at least one injection portin a delivery catheter such that said autologous growth factorcomposition wets the stent graft disposed within the delivery catheter.

In another embodiment of the method for providing a stent graft and acell growth-promoting composition, the method further comprisesproviding a drug in combination with the autologous growth factorcomposition wherein the drug is selected from the group consisting ofsmall molecules, peptides, proteins, hormones, DNA or RNA fragments,cells, genetically engineered cells, genes, cell growth promotingcompositions, matrix metalloproteinase inhibitors, antibiotics,cyclooxygenase-2 inhibitors, angiotensin-converting enzyme inhibitors,glucocorticoids, beta blockers, nitric acid synthase inhibitors,antioxidants and cellular adhesion molecules.

In yet another embodiment of the method for providing a stent graft anda cell growth-promoting composition, the activating step comprisesmixing said PRP with an activating agent such as, but not limited to, aplatelet agonist. In one embodiment the platelet agonist is adenosinediphosphate (ADP), preferably at a concentration of 5 to 20 μM, orthrombin receptor activating peptide (TRAP), preferably at aconcentration of 5 to 10 μM.

In an embodiment of the method for providing a stent graft and a cellgrowth-promoting composition, the autologous growth factor compositionis centrifuged to remove cells and cellular particulates prior to thecoating step.

In another embodiment of the method for providing a stent graft and acell growth-promoting composition, the said treatment site is ananeurysm site

In another embodiment of the method for providing a stent graft and acell growth-promoting composition, the stent graft is pre-coated with abase coating material selected from the group consisting of heparin,hyaluronate, alginate, collagen, fibrin, dextran, β-cyclodextrin,polyvinyl alcohol and hydrogel prior to coating with said autologousgrowth factor composition.

Another embodiment according to the present invention provides adelivery catheter for delivering a stent graft to a vessel in a patientin need thereof, having disposed therein a stent graft, comprising atleast one injection port through which coating composition(s) areinjected to coat the stent graft. In another embodiment, the coatingcomposition(s) is autologous growth factor composition or a pre-coatingmaterial.

In another embodiment of the delivery catheter, the delivery cathetercomprises a plurality of injection ports wherein the plurality ofinjection ports are disposed along the length of the delivery cathetersuch that the entire stent graft is accessible by the plurality ofinjection ports.

One embodiment of the present invention provides an endothelializationpromoting stent graft for implantation into a patient in need thereofcomprising a stent graft having an autologous growth factor compositiondeposited thereon.

In an embodiment of the endothelialization promoting stent graft, thestent graft further comprises a base coat between the stent graft andthe autologous growth factor composition coating wherein the base coatcomprises a material selected from the group consisting of heparin,hyaluronate, alginate, collagen, fibrin, dextran, β-cyclodextrin,polyvinyl alcohol and hydrogen.

In another embodiment of the endothelialization promoting stent graft,the autologous growth factor composition is isolated from the patient atthe time of stent graft implantation. In yet another embodiment, thestent graft is coated with the autologous growth factor composition atthe time of stent graft implantation.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 depicts a fully deployed stent graft with an exterior metalscaffolding as used in one embodiment according to the presentinvention.

FIGS. 2 a-b depict a stent graft delivery catheter containing injectionports for coating the stent graft with autologous growth factorcomposition(s) immediately prior to deployment in accordance with theteachings of the present invention. FIG. 2 b is a cross-section of thestent graft delivery catheter depicted in FIG. 2 a.

FIG. 3 depicts the effects of autologous platelet gel on humanmicrovascular endothelial cell proliferation.

FIG. 4 depicts the effects of autologous platelet gel on arterial smoothmuscle cell proliferation.

FIG. 5 depicts the effects of autologous platelet gel on endothelialcell migration.

DEFINITION OF TERMS

Prior to setting forth embodiments according to the present invention,it may be helpful to an understanding thereof to set forth definitionsof certain terms that will be used hereinafter. Unless otherwiseexplained, all technical and scientific terms used herein have the samemeaning as commonly understood by one of ordinary skill in the art towhich this invention belongs. The singular terms “a,” “an,” and “the”include plural referents unless context clearly indicates otherwise.Similarly, the word “or” is intended to include “and” unless the contextclearly indicates otherwise. The term “comprises” means “includes.”

Activating Agent(s): As used herein, “activating agent(s)” shall includeplatelet agonist(s) that are capable of inducing platelet activationwhich lead to platelet degranulation and release of growth factorsstored within alpha granules. Exemplary, non-limiting examples ofactivating agents include adenosine diphosphate (ADP) and thrombinreceptor agonist peptide (TRAP).

Animal: As used herein, “animal” shall include, without limitation,mammals, fish, reptiles and birds. Mammals include, but are not limitedto, primates, including humans, dogs, cats, goats, sheep, rabbits, pigs,horses and cows.

Autologous Growth Factor Composition: As used herein, “autologous growthfactor composition” includes to growth factors released from plateletsafter activation of the platelets with an activating agent. Autologousgrowth factor composition can refer to a composition that eithercontains, or have been centrifuged to remove, platelet cellular materialafter activation.

Biocompatible: As used herein “biocompatible” refers to any materialthat does not cause injury or death to the animal or induce an adversereaction in an animal when placed in intimate contact with the animal'stissues. Adverse reactions include, without limitation, inflammation,infection, fibrotic tissue formation, cell death, embolizations and/orthrombosis.

Bioactive Material: As used herein, “bioactive material(s)” shallinclude any compound or composition that creates a physiological and/orbiological effect in an animal. Non-limiting examples of bioactivematerials include small molecules, peptides, proteins, hormones, DNA orRNA fragments, genes, cells, genetically-modified cells, cell growthpromoting compositions, matrix metalloproteinase inhibitors, autologousplatelet gel, platelet rich plasma, either inactivated or activated,other natural and synthetic gels, such as, without limitation,alginates, collagens, and hyaluronic acid, polyethylene oxide,polyethylene glycol, and polyesters, as well as combinations of thesebioactive materials.

Cell Growth Promoting Compositions: As used herein, “cell growthpromoting factors” or “cell growth promoting compositions” shall includeany bioactive material having a growth promoting effect on vascularcells. Non-limiting examples of cell growth promoting compositionsinclude vascular endothelial growth factor (VEGF), platelet-derivedgrowth factor (PDGF), platelet-derived epidermal growth factor (PDEGF),fibroblast growth factors (FGFs), transforming growth factor-beta(TGF-β), platelet-derived angiogenesis growth factor (PDAF) andautologous platelet gel (APG) including platelet rich plasma (PRP),platelet poor plasma (PPP) and thrombin.

Drug(s): As used herein, “drug” shall include any bioactive compound orcomposition having a therapeutic effect in an animal. Exemplary, nonlimiting examples include small molecules, peptides, proteins, hormones,DNA or RNA fragments, genes, cells, genetically-modified cells, cellgrowth promoting compositions, matrix metalloproteinase inhibitors,antibiotics, cyclooxygenase-2 inhibitors, angiotensin-converting enzymeinhibitors, glucocorticoids, beta blockers, nitric acid synthaseinhibitors, antioxidants, cellular adhesion molecules, and autologousplatelet composition.

Endoleak: As used herein, “endoleak” refers to the presence of bloodflow past the seal between an end of the stent graft and the vesselwall, and into the aneurysmal sac, when all such flow should becontained within its lumen.

Implantable Medical Device: As used herein, “implantable medical device”includes, without limitation, stents and stent grafts used in the repairof vascular injuries.

Migration: As used herein, “migration” refers to displacement of a stentor stent graft sufficient to be associated with a complication, forexample, endoleak.

Treatment Site and Administration Site: As used herein, the phrases“treatment site” and “administration site” includes a portion of avessel having a stent or a stent graft positioned in its vicinity. Atreatment site can be, without limitation, an aneurysm site, the site ofan acute traumatic aortic injury, the site of vessel narrowing or othervascular-associated pathology.

DETAILED DESCRIPTION

Embodiments according to the present invention provide devices andrelated methods useful for preventing post-implantation migration ofimplantable vascular devices using autologous growth factor compositionto promote implantable vascular device attachment to blood vesselluminal walls. A delivery device, which allows the application ofautologous growth factor compositions to the stent graft while the stentgraft is disposed within the delivery device, prior to the deployment ofthe stent graft is provided.

For convenience, the devices and related methods according to thepresent invention discussed hereinafter will be exemplified using stentgrafts intended to treat aneurysms. As discussed briefly above, ananeurysm is a swelling, or expansion of a blood vessel lumen at adefined point and is generally associated with a vessel wall defect.Aneurysms are often a multi-factorial asymptomatic vessel disease thatif left unchecked may result in spontaneous rupture, often with fatalconsequences. Previous methods to treat aneurysms involved highlyinvasive surgical procedures where the affected vessel region wasremoved and replaced with a synthetic graft that was sutured in place.However, this procedure was extremely risky and was generally onlyemployed in otherwise healthy vigorous patients who were expected tosurvive the associated surgical trauma. Elderly and more feeble patientswere not candidates for many aneurysmal surgeries and remained untreatedand thus at continued risk for sudden death.

In order to overcome the risks associated with invasive aneurysmalsurgeries, stent grafts were developed that can be deployed with a cutdown procedure or percutaneously using minimally invasive procedures.Essentially, a catheter having a stent graft compressed and fitted intothe catheter's distal tip is advanced through an artery to theaneurysmal site. The stent graft is then deployed within the vessellumen juxtaposed to the weakened vessel wall forming an inner liner thatinsulates the aneurysm from the body's hemodynamic forces therebyreducing, or eliminating the possibility of rupture. The size and shapeof the stent graft is matched to the treatment site's lumen diameter andaneurysm length. Moreover, branched grafts are commonly used to treatabdominal aortic aneurysms that are located near the iliac branch.

Stent grafts generally comprise a metal scaffolding having abiocompatible covering such a Dacron® (E.I. du Pont de Nemours &Company, Wilmington, Del.) or a fabric-like material woven from avariety of biocompatible polymer fibers. Other embodiments includeextruded sheaths and coverings. The scaffolding is generally on theluminal wall-contacting surface of the stent graft and directly contactsthe vessel lumen. The sheath material is stitched, glued or molded ontothe scaffold. In other embodiments, the scaffolding may be on thegraft's blood flow contacting surface or interior. When a self-expandingstent graft is deployed from the delivery catheter, the scaffoldingexpands to fill the lumen and exerts circumferential force against thelumen wall. This circumferential force is generally sufficient to keepthe stent-g raft from migrating and thus preventing endoleak. However,stent migration and endoleak may occur in vessels that have irregularshapes or are shaped such that they exacerbate hemodynamic forces withinthe lumen. Stent migration refers to a stent graft moving from theoriginal deployment site, usually in the direction of the blood flow.Endoleak (as used herein) refers specifically to the seepage of bloodaround the stent ends to pressurize the aneurysmal sac or between thestent graft and the lumen wall. Stent graft migration may result in theaneurysmal sac being exposed to blood pressure again and increasing therisk of rupture. Endoleaks occur in in a small percentage of aneurysmstreated with stent grafts. Therefore, it would be desirable to havedevices, compositions and methods that minimize post implantation stentgraft migration and endoleak.

Co-pending U.S. patent application Ser. No. 10/977,545, filed Oct. 28,2004 discloses injecting autologous platelet gel (APG) into theaneurysmal sac and/or between an implanted stent graft and the vesselwall to induce endothelialization of the stent graft to prevent endoleakand stent graft migration. Autologous platelet gel is produced byactivating autologous platelet-rich plasma with thrombin to form a gelcontaining an increased concentration of growth factors over unactivatedplatelet rich plasma (PRP). However, the APG is extremely viscous andcannot be injected after formation. Therefore, the components of APG,PRP and thrombin, must be co-injected at the treatment site such thatAPG is formed in situ. The present inventors sought to provide anautologous growth factor-containing composition which is less viscousthan APG and can be used to coat a stent graft prior to implantation.The autologous growth factor composition of the present invention,wherein PRP is activated to produce growth factors in the absence ofthrombin, is a liquid composition which can be used to coat a stentgraft prior to deployment and implantation. This approach is especiallybeneficial because it avoids the potential embolization concernsassociated with thrombin use.

Activation of PRP, either by thrombin or the activating agents adenosinediphosphate or thrombin receptor activating peptide, produces a cocktailof growth factors, the composition of which is not dependent on the typeof activation. Therefore activation of PRP by thrombin or anotheractivating agent, produces an equivalent composition of growth factors.

In one embodiment, autologous growth factor compositions areadministered to a treatment site within a vessel lumen as a coating on astent graft. The vessel wall's blood-contacting lumen surface comprisesa layer of endothelial cells. In the normal mature vessel theendothelial cells are quiescent and do not multiply. Thus, a stent graftcarefully placed against the vessel wall's blood-contacting luminalsurface rests against a quiescent endothelial cell layer. However, ifcell growth-promoting compositions are administered with the stentgraft, the normally quiescent endothelial cells lining the vessel wall,and in intimate contact with the stent graft luminal wall contactingsurface, will be stimulated to proliferate. The same will occur withsmooth muscle cells and fibroblasts found within the vessel wall. Asthese cells proliferate they will grow into and around the stent graftlining such that the stent graft becomes physically attached to thevessel lumen rather than merely resting against it. In one example, thestent graft has a metallic scaffolding on the graft's luminal wallcontacting surface and the cell growth-promoting factor is an autologousgrowth factor composition.

The autologous growth factor composition comprises activated platelets,unactivated platelets, and platelet releasate(s) and it is obtained byactivating platelets in autologous PRP to release their contents (i.e.,platelet releasates). Platelets are cytoplasmic portions of marrowmegakaryocytes which have no nucleus for replication and an expectedlifetime of five to nine days. Upon activation by a variety ofactivating agents, platelets release pre-formed stores of growth factorsfrom alpha granules. A wide variety of growth factors are released byactivated platelets including, but not limited to, platelet-derivedgrowth factor (PDGF), platelet-derived epidermal growth factor (PDEGF),fibroblast growth factor (FGF), transforming growth factor-beta (TGF-β),insulin-like growth factor (IGF) and platelet-derived angiogenesisgrowth factor (PDAF). These growth factors have been implicated in woundhealing by increasing the rate of collagen secretion, vascular in-growthand fibroblast proliferation. Platelet rich plasma also contains aconcentrated population of white blood cells (WBC) which, followingactivation, secrete a variety of factors, including but not limited to,growth factors, cytokines, chemokines, prostaglandins, and matrixmetalloproteinases. Non-limiting examples of growth factors releasedfrom WBCs include IGF, basic FGF, TGF and others. Non-limiting examplesof cytokines released from WBCs include, granulocyte colony stimulatingfactor (G-CSF), granulocyte macrophage colony stimulating factor(GM-CSF) and others. Many of these WBC-derived factors are also capableof promoting proliferation and enhancing migration of a variety of celltypes.

Platelet-rich plasma is generated from variable speed centrifugation ofautologous blood using devices such as, but not limited to, theMagellan™ Autologous Platelet Separator System (Medtronic, Inc.,Minneapolis, Minn.). The Magellan™ Separator is a small, portableplatelet separator suitable for use in a variety of clinical settings,including an operating room. Additionally, the Magellan™ system isparticularly suited for producing PRP from a small amount of autologousblood in a closed system that minimizes contamination.

In one embodiment, the autologous growth factor composition is formedfrom PRP mixed with one or more activating agents for about 5, about 10,or about 15 minutes. In one specific example, the autologous growthfactor composition is formed from PRP mixed with an activating agent forabout 10 minutes. In some embodiments, the autologous growth factorcomposition is further centrifuged to remove some or all of theplatelets in the mixture after activation and prior to coating the stentgraft.

Activating agents are platelet agonists such as adenosine diphosphate(ADP) or thrombin receptor activating peptide (TRAP). In someembodiments, the autologous growth factor composition is formed from PRPmixed with about 5 to about 20 μM, about 7 to about 18 μM, about 9 toabout 17 μM, or about 11 to about 15 μM of ADP. In one example, theautologous growth factor composition is formed from PRP mixed with about10 μM of ADP. In some other embodiments, the autologous growth factorcomposition is formed from PRP mixed with about 5 to about 10 μM, about6 to about 9 μM, or about 7 to about 8 μM of TRAP. In one specificexample, the autologous growth factor composition is formed from PRPmixed with about 7 μM of TRAP.

Implantable medical devices, specifically stent grafts, areadvantageously sealed to the vessel lumen using the autologous growthfactor composition. Once associated with the stent graft, the autologousgrowth factor composition, with its rich composition of growth andhealing factors, can promote the integration of the stent graft into thevessel wall. Enhanced healing and tissue in-growth from the surroundingvessel may lessen the chances of stent graft migration and endoleak.Additionally, drugs that induce positive effects at the aneurysm sitecan also be delivered with autologous growth factor composition and themethods described.

Because of the physical properties of the autologous growth factorcomposition, it is particularly useful in promoting endothelializationof vascular stent grafts. The autologous growth factor composition notonly can coat the exterior surface of the stent graft but also fills thepores of the stent graft, inducing migrating cells into the stent graftfabric. As a result, engraftment of endothelial cells will occurpreferentially at those sites where autologous growth factor compositionis present. Previously, vascular prostheses were seeded withnon-autologous materials, enhancing the possibility of graft rejection.Autologous growth factor composition will not cause antigenicity orrejection effects.

Endothelialization may be stimulated by induced angiogenesis resultingin formation of new capillaries in the interstitial space and surfaceendothelialization. This has led to modification of medical devices withvascular endothelial growth factor (VEGF) and fibroblast growth factors1 and 2 (FGF-1, FGF-2). The discussion of these factors is for exemplarypurposes only, as those of skill in the art will recognize that numerousother growth factors have the potential to induce cell-specificendothelialization. VEGF is endothelial cell-specific however it is arelatively weak endothelial cell mitogen. FGF-1 and FGF-2 are morepotent mitogens but are less cell specific. The development ofgenetically-engineered growth factors is anticipated to yield morepotent endothelial cell-specific growth factors. Additionally it may bepossible to identify small molecule drugs that can induceendothelialization.

Additional embodiments provide coatings for stent grafts thatincorporate endothelialization factors in addition to the autologousgrowth factor composition. Stent grafts can be coated withendothelialization factors, including growth factors and drugs. Thefield of medical device coatings is well established and methods forcoating stent grafts with bioactive compositions, with or without addedpolymers, are well known to those of skill in the art.

The autologous growth factor composition is generated and applied to thestent graft in the operating room immediately prior to deployment andimplantation of the stent graft. In one embodiment, activation agentsare added to the PRP and the resultant growth factor-rich plasma, theautologous growth factor composition, is applied directly to a stentgraft loaded within a delivery device, such as a delivery catheter.

The stent graft is optionally pre-coated with a material to enhancegrowth factor attachment to the stent graft including, but not limitedto, heparin, hyaluronate, alginate, collagen, fibrin, dextran,β-cyclodextrin, polyvinyl alcohol hydrogel.

In one embodiment, the stent graft is provided “pre-loaded” into adelivery catheter and the autologous growth factor composition isapplied to the stent graft while the stent graft is disposed within thedelivery catheter. In normal stent deployment protocols, a vascularstent graft 100 is fully deployed through the left iliac artery 114 toan aneurysm site 104 (FIG. 1). Stent graft 100 has a distal end 102 andan iliac leg 108 to anchor the stent graft in the iliac artery 116.Stent graft 100 is deployed first in a first delivery catheter and theiliac leg 108 is deployed in a second delivery catheter. The stent graft100 and iliac leg 108 are joined with a 2 cm overlap of the two segments106.

A stent graft is pre-loaded into a delivery catheter such as thatdepicted in FIG. 2 a. Stent graft 100 is radially compressed to fill thestent graft chamber 218 in the distal end 202 of delivery catheter 200.The stent graft 100 is covered with a retractable sheath 220. Catheter200 has two injection ports 208 and 210 for delivering the autologousgrowth factor composition to the compressed stent graft. In thisembodiment, the autologous growth factor composition is injected througheither or both of injection ports 208 and 210 to wet stent graft 100.Stent graft 100 is then deployed to the treatment site as depicted inFIG. 1. FIG. 2 b depicts a cross-sectional view of stent graft 100loaded into the delivery catheter 200 and the delivery catheter'sretractable sheath 220 illustrating an injection port 208, 210 fordelivering autologous growth factor composition to stent graft 100.

In an additional embodiment, the stent graft is pre-coated with amaterial to enhance attachment of growth factors from autologous growthfactor composition, either prior to or after the stent graft is loadedinto the delivery catheter. The stent graft can be pre-coated usingstandard coating methods including, but not limited to, dipping andspraying. Alternatively, the pre-coat can be applied through injectionports 208 and/or 210 prior to the application of the autologous growthfactor composition.

The following examples are meant to illustrate one or more embodimentsaccording to the invention and are not meant to limit the scope of theinvention to that which is described below.

EXAMPLE 1 Properties of Platelet Rich Plasma

Aliquots of human peripheral blood (30-60 mL) are passed through theMagellan™ Autologous Platelet Separator System (the Magellan™ system,Medtronic, Inc., Minneapolis, Minn.) and the concentrated, platelet-richplasma fraction (PRP) assayed for platelets (PLT), white blood cells(WBC) and hematocrit (Hct) (Table 1). The Magellan™ system concentratedplatelets and white blood cells six-fold and three-fold respectively.TABLE 1 Blood cell yields after passing through the Magellan ™ system.Mean ± SD n = 19 Initial Blood PRP Yield PLT (×1000/μL) 220.03 ± 48.58 1344.89 ± 302.00  6.14 ± 0.73 WBC 5.43 ± 1.43 17.04 ± 7.01  3.12 ± 0.90(×1000μ/L) Hct (%) 38.47 ± 2.95  6.81 ± 1.59Cell Yield = cell count in PRP/cell count in initial blood = [timesbaseline]

Additionally, PRP was assayed for levels of the endogenous growthfactors platelet-derived growth factor (PDGF), transforming growthfactor-beta (TGF-β), basic fibroblast growth factor (bFGF), vascularendothelial growth factor (VEGF), and endothelial growth factor (EGF).As a result of increased platelet and white blood cell counts in PRP,increased concentrations of growth factors were found. TABLE 2 GrowthFactor Content of Blood and PRP Mean ± SD; n = 9 Initial Blood PRPPDGF-AB (ng/mL) 10.2 ± 1.4  88.4 ± 28.8 PDGF-AA (ng/mL) 2.7 ± 0.5 22.2 ±4.2  PDGF-BB (ng/mL) 5.8 ± 1.4 57.8 ± 36.6 TGF-β1 (ng/mL) 41.8 ± 9.5 231.6 ± 49.1  bFGF (pg/mL) 10.7 ± 2.9  48.4 ± 25.0 VEGF (pg/mL) 83.1 ±65.5 597.4 ± 431.4 EGF (pg/mL) 12.9 ± 6.2  163.3 ± 49.4 

EXAMPLE 2 Autologous Platelet Gel Generation

Autologous Platelet Gel (APG) is generated from the PRP fractionproduced in the Magellan™ system by adding thrombin and calcium toactivate the fibrinogen present in the PRP as well as causing theplatelets to release additional stores of growth factors. For eachapproximately 7-8 mL of PRP, approximately 5000 units of thrombin in 5mL 10% calcium chloride are required for activation. The APG is formedimmediately upon mixing of the activator solution with the PRP. Theconcentration of thrombin can be varied from approximately 1-1,000 U/mL,depending on the speed required for setting to occur. The lowerconcentrations of thrombin will provide slower gelling times.

EXAMPLE 3 Effects of Platelet Releasates on Cell Proliferation

A series of in vitro experiments were conducted evaluating the effect ofreleased factors from platelets on the proliferation of the humanmicrovascular endothelial cells and human coronary artery smooth musclecells. Primary cell cultures of both cell types were establishedaccording to protocols well known to those skilled in the art of cellculture. Autologous platelet gel was used as the source of plateletreleasates. For each cell type, five culture conditions were evaluated;basal medium (BM)+APG; BM+platelet-free plasma (PFP); growth medium(GM); BM alone; and BM+thrombin. Growth medium is the standard culturemedium for the cell type and contains optimal growth factors andsupplements.

Autologous platelet gel had a significant growth effect on humanmicrovascular endothelial cells after four days of culture (FIG. 3) andon human coronary artery smooth muscle cells after five days of culture(FIG. 4).

EXAMPLE 4 Effect of APG on Endothelial Cell Migration

Human microvascular endothelial cell migration was performed in a Boydenchemotaxis chamber which allows cells to migrate through 8 μm pore sizepolycarbonate membranes in response to a chemotactic gradient. Humanmicrovascular endothelial cells (5×10⁵) were trypsinized, washed andresuspended in serum-free medium (DMEM) and 400 μL of this suspensionwas added to the upper chamber of the chemotaxis assembly. The lowerchamber was filled with 250 μL serum-free DMEM containing either 10%APG-derived serum, 10% PFP-derived serum or DMEM alone. After apre-determined amount of time, the filters were removed and the cellsremaining on the upper surface of the membrane (cells that had notmigrated through the filter) were removed with a cotton swab. Themembranes were then sequentially fixed, stained and rinsed to enable thevisualization and quantification of cells that had migrated through thepores to the other side of the membrane. The number of migrated cellswas significantly higher in the 10% APG serum culture than the basalmedium or 10% platelet-free serum cultures (FIG. 5).

Unless otherwise indicated, all numbers expressing quantities ofingredients, properties such as molecular weight, reaction conditions,and so forth used in the specification and claims are to be understoodas being modified in all instances by the term “about.” Accordingly,unless indicated to the contrary, the numerical parameters set forth inthe following specification and attached claims are approximations thatmay vary depending upon the desired properties sought to be obtained.Each numerical parameter should at least be construed in light of thenumber of reported significant digits and by applying ordinary roundingtechniques. Notwithstanding that the numerical ranges and parameterssetting forth the broad scope of embodiments according to the inventionare approximations, the numerical values set forth in the specificexamples are reported as precisely as possible. Any numerical value,however, inherently contains certain errors necessarily resulting fromthe standard deviation found in their respective testing measurements.

Recitation of ranges of values herein is merely intended to serve as ashorthand method of referring individually to each separate valuefalling within the range. Unless otherwise indicated herein, eachindividual value is incorporated into the specification as if it wereindividually recited herein. All methods described herein can beperformed in any suitable order unless otherwise indicated herein orotherwise clearly contradicted by context.

Groupings of alternative elements or embodiments are not to be construedas limitations. Each group member may be referred to and claimedindividually or in any combination with other members of the group orother elements found herein. It is anticipated that one or more membersof a group may be included in, or deleted from, a group for reasons ofconvenience and/or patentability. When any such inclusion or deletionoccurs, the specification is herein deemed to contain the group asmodified thus fulfilling the written description of all Markush groupsused in the appended claims.

Embodiments according to the invention are described herein, variationson those embodiments will become apparent to those of ordinary skill inthe art upon reading the foregoing description.

Furthermore, numerous references have been made to patents and printedpublications throughout this specification. Each of the above citedreferences and printed publications are herein individually incorporatedby reference in their entirety.

It is to be understood that the embodiments according to the inventiondisclosed herein are illustrative and that other modifications may beemployed. Thus, by way of example, but not of limitation, alternativeconfigurations may be utilized in accordance with the teachings herein.

1. A method for providing a stent graft and a cell growth-promotingcomposition comprising: obtaining autologous platelet rich plasma (PRP)from a patient in need of a stent graft; activating said PRP to formautologous growth factor composition; coating said stent graft with saidautologous growth factor composition; and implanting said autologousgrowth factor composition-coated stent graft into a vessel at atreatment site in a patient wherein said autologous growth factorcomposition-coated stent graft induces endothelialization of said stentgraft.
 2. The method of claim 1 wherein said coating step comprisesinjecting autologous growth factor composition through at least oneinjection port in a delivery catheter such that said autologous growthfactor composition wets said stent graft disposed within said deliverycatheter.
 3. The method of claim 1 further comprising providing a drugin combination with said autologous growth factor composition whereinsaid drug is selected from the group consisting of small molecules,peptides, proteins, hormones, DNA or RNA fragments, cells, geneticallyengineered cells, genes, cell growth promoting compositions, matrixmetalloproteinase inhibitors, antibiotics, cyclooxygenase-2 inhibitors,angiotensin-converting enzyme inhibitors, glucocorticoids, betablockers, nitric acid synthase inhibitors, antioxidants and cellularadhesion molecules.
 4. The method of claim 1 wherein said activatingstep comprises mixing said PRP with an activating agent
 5. The method ofclaim 4 wherein said activating agent is a platelet agonist.
 6. Themethod of claim 5 wherein said platelet agonist is adenosine diphosphate(ADP) or thrombin receptor activating peptide (TRAP).
 7. The method ofclaim 6 wherein said platelet agonist is 5 to 20 μM of said ADP.
 8. Themethod of claim 6 wherein said platelet agonist is 5 to 10 μM of saidTRAP.
 9. The method of claim 1 wherein said autologous growth factorcomposition is centrifuged to remove cells and cellular particulatesprior to said coating step.
 10. The method of claim 1 wherein saidtreatment site is an aneurysm site
 11. The method of claim 1 whereinsaid stent graft is pre-coated with a base coating material selectedfrom the group consisting of heparin, hyaluronate, alginate, collagen,fibrin, dextran, β-cyclodextrin, polyvinyl alcohol and hydrogel prior tocoating with said autologous growth factor composition.
 12. A deliverycatheter for delivering a stent graft to a vessel in a patient in needthereof, having disposed therein a stent graft, comprising at least oneinjection port through which coating composition(s) are injected to coatsaid stent graft.
 13. The delivery catheter according to claim 12wherein said coating composition(s) is autologous growth factorcomposition or a pre-coating material.
 14. The delivery catheteraccording to claim 12 comprising a plurality of injection ports.
 15. Thedelivery catheter according to claim 14 wherein said plurality ofinjection ports are disposed along the length of said delivery cathetersuch that the entire stent graft is accessible by said plurality ofinjection ports.
 16. An endothelialization promoting stent graft forimplantation into a patient in need thereof comprising a stent grafthaving an autologous growth factor composition deposited thereon. 17.The endothelialization promoting stent graft according to claim 16further comprising a base coat between said stent graft and saidautologous growth factor composition coating wherein said base coatcomprises a material selected from the group consisting of heparin,hyaluronate, alginate, collagen, fibrin, dextran, β-cyclodextrin,polyvinyl alcohol and hydrogen.
 18. The endothelialization promotingstent graft according to claim 16 wherein said autologous growth factorcomposition is isolated from said patient at the time of stent graftimplantation.
 19. The endothelialization promoting stent graft accordingto claim 16 wherein said stent graft is coated with said autologousgrowth factor composition at the time of stent graft implantation.